1. Field of the Invention
The invention relates to an apparatus for the agglomeration of feed material with thermoplastic properties, comprising a radially symmetrical chamber delimited peripherally by a perforated die and at its end faces by a front wall element and a rear wall element, and comprising an agglomerating vane supported in the hollow chamber so as to be rotatable about the longitudinal axis of the hollow chamber and forming with its leading side in the rotational direction together with the two wall elements and the perforated die at least one revolving agglomeration chamber.
The invention further relates to a disc-shaped or ring-shaped wear element suitable for use with an apparatus of the aforementioned kind for delimiting a hollow chamber of radial symmetry.
2. Description of the Related Art
In the course of reutilization of waste material, the recycling of thermoplastic materials, e.g., films, fibers, filaments etc. made of plastic materials, gains more and more importance. In this connection, the thermoplastic waste material is transformed into an intermediate product in the form of granules which are then returned into the production process as starting material for use in extruders, injection molding machines and similar equipment.
During the expert treatment of thermoplastic waste material in an apparatus of the aforementioned kind, the feed material is always subjected to high agglomeration and shearing forces causing a great heat development within the agglomerator. This effect is desired within a temperature range below the type-specific melting point of the feed material since only by means of this heat development agglomeration is made possible. If during agglomeration the material-specific melting point is exceeded, there will be an irreversible alteration of the mechanical properties of the feed material which makes the valuable starting material unusable for further processing.
An apparatus for the agglomeration of thermoplastic wastes of the aforementioned kind is described in German Patent Specifications 26 14 730 C2 and 197 06 371 A1. These references disclose a disc-shaped annular chamber which is enclosed by a perforated die and into which the feed material is fed in the axial direction. A coaxially arranged agglomerating vane rotates in this chamber and forms with its effective flanks two revolving agglomeration chambers. The heat generated during compaction or agglomeration leads to a plasticizing of the feed material which, in turn, effects the passage of the feed material through the perforations of the die. To avoid thermal damage of the feed material, the agglomerator is equipped with a cooling system for dissipating the excess heat developed during the agglomeration and, in this way, the working temperature of the agglomerator is maintained within a range which is not critical to the feed material.
From the German Patent Specification 38 42 072 C1 an agglomerator is already known which differs from the already mentioned agglomerators insofar as the radially symmetrical chamber narrows radially towards the perforated die. This effects a three-dimensional processing of the feed material thus intensifying the compacting and plasticizing of the feed material and increasing in this way the specific throughput efficiency.
It is an object of the present invention to improve the known agglomerators so that the efficiency of the apparatus is increased without affecting negatively the heat generated in the agglomerator.
In accordance with the present invention, this is achieved in connection with the apparatus in that the surfaces of the front and/or rear wall elements facing the radially symmetrical chamber have profiles running from the inside to the outside for the transport of the feed material.
In accordance with the present invention, this is further achieved in connection with the wear element in that the wear element is configured to confine a radially symmetrical chamber wherein the wear element has profiles running from the inside to the outside.
The arrangement of the profiles on the inner surface of the wall elements according to the invention leads to a mostly defined flow of the feed material within the radially symmetrical chamber. In this connection, the feed material is moved on the shortest possible path along the profiles to the peripheral area of the hollow chamber where the actual plasticization and agglomeration takes place. In this way it is prevented that parts of the feed material reside too long in the central area of the hollow chamber where, even though they are entrained by the agglomerating vane, reach the plasticization area of the compacting chamber too slowly and are thus exposed to the high temperatures longer than necessary.
The configuration of the circular disc-shaped hollow chamber according to the invention achieves a forced material flow resulting in a shorter residence time of the feed material in the radially symmetrical hollow chamber. This provides, on the one hand, the advantage that, due to the shortened exposure time, the thermal stress is reduced and, accordingly, the danger of thermal damage to the feed material is minimized. On the other hand, the shortened residence time of the feed material in the agglomerator leads to a higher material throughput and thus to an increase of the efficiency of the agglomerator over all.
According to the invention, the profiles are preferably grooves worked into the inner surface of the wall elements. In this connection, the efficiency and thus the suitability of the grooves for the material transport depend mostly on their configuration details to be explained in the following.
The configuration of the grooves according to the invention provides the advantage of interacting with the rotating agglomerating vane which effects the advance of the feed material within the grooves during its rotation. Accordingly, the grooves according to a preferred embodiment have a longitudinal, plane guiding surface which acts counter to the rotating direction of the agglomerating vane such that the feed material being rotated by the agglomerating vane reaches the grooves and comes into contact with the guiding surface thereat. This prevents the feed material from continuously rotating and forces the feed material to change its direction of movement so that movement is parallel to the orientation of the grooves. The advance of the feed material is effected by the outer edges of the agglomerating vane; the outer edges define an intersecting point with the grooves, which point moves outwardly during rotation.
Compared to other configurations, the groove with a plane guiding surface has the advantage that its efficiency is not much impaired even after the first signs of wear are detected. In contrast to this, in the case of grooves having, for example, a concave cross-section, wear very quickly leads to small intersection angles xcex1 of the groove with the inner surface of the wall elements, and the efficiency of the guiding surface is thus lost in this way.
Good results are obtained with grooves having a guiding surface which forms with the inner surface of the wall elements an angle xcex1 of 60 to 90xc2x0, wherein the optimum angle xcex1 always depends on the type of feed material and the specific configuration of the agglomerator.
In a further embodiment of the invention, the guiding surface forms with only one further plane surface the groove according to the invention, so that the groove has a triangular cross-section. The surfaces constituting the groove form preferably an angle xcex2 of 70 to 110xc2x0. The preferred angle xcex2 of 90xc2x0 provides, in addition to a good material flow, further advantages with regard to a simple manufacture of such a groove.
Another embodiment of the invention is moreover preferred, in which the outer border of the groove is formed by a concave surface which is a continuous extension of the guiding surface. This measure offers the advantage that the outwardly directed material flow, when leaving the groove, undergoes a directional change counter to the rotational direction of the agglomeration vane and thus enhances the compaction and plasticization process considerably.
Apart from the special configuration of the grooves, their arrangement on the inner surface of the wall elements enclosing the radially symmetrical hollow chamber is of utmost importance for a rapid material flow within the agglomerator. An arrangement of the grooves on the inner surface of the wall elements, wherein the grooves form an angle xcex3 of approximately 90xc2x0 with the front side of the agglomerating vane, in the direction of rotation of the agglomerating vane, has proven to be especially suitable because in this configuration the feed material is advanced by the conveying edges of the agglomerating vane parallel to the direction of extension of the grooves. Due to the specific curvature of the front side of the agglomerating vane, an angle xcex3 of 90xc2x0 cannot generally be realized over the whole length of the groove. A good transport of the feed material by the agglomerating vane is achieved with an angle xcex3 of 70xc2x0 to 110xc2x0.
The invention comprises also a disc-shaped or ring-shaped wear element whose end faces facing the hollow chamber show the above described profiles and which thus can claim all the mentioned advantages. Moreover, the use of a wear element according to the present invention within an agglomerator offers the advantage that, when wear is at an advanced state, the quantity of parts to be replaced is limited to a minimum. It is furthermore possible to have the wear parts made of an especially wear-resistant material in order to increase the service life of the wear parts without increasing the production cost of the agglomerator significantly.
According to a further embodiment of the invention, the side walls (cooling disc and cooling ring), onto which the wear parts are fastened, are provided with channels suitable for receiving a coolant, so that excessive heat generation can be counteracted as closely as possible to the location of origin of the heat.